It’s Your first and last line of defense for your PC.
While these ports allow you to download your favorite music or surf your favorite site, they also expose your computer to attacks from malicious programs. A firewall is your personal army of guards at these doors.
The firewall’s job is to know the difference between good traffic you want to let in, and bad traffic you want to keep out. To do this, it has to watch all traffic coming in and going out of the doors. A simple idea, but a complicated job.
Some firewalls are better than others, and a ZoneAlarm firewall is the hands-down the most effective firewall on the market.